A flowmeter having a measuring tube implements a measuring principle for measuring the flow of a medium through the measuring tube and measures the flow according to the measuring principle during operation. The volume flow and the mass flow of the medium through the measuring tube are thereby designated as flow.
The measuring accuracy of a flowmeter is, in particular, determined using the zero flow through the measuring tube. The zero flow is the flow that is measured by the flowmeter when a medium is not flowing through the measuring tube. If the zero flow is not equal to zero, then the flow of the flowing medium measured by the flowmeter is afflicted with a constant error in the amount of the zero flow. Accordingly, a zero flow not equal to zero causes a constant measurement error.
Thus, the object of the invention is to provide a method for operating a flowmeter as well as a flowmeter, in which a measurement error caused by a zero flow not equal to zero is at least reduced.
According to a first teaching, the invention relates to a method for operating a flowmeter, in which the derived and shown object is achieved. The method according to the invention is initially and essentially characterized by the following method steps: In a first method step, in each case, a continuous dwell time of the measured flow greater than or equal to a flow threshold is assigned to a flow interval and a flow volume is determined from the measured flow in the flow interval. In a second method step, in each case, a continuous dwell time of the measured flow less than the flow threshold is assigned to a zero flow interval. In a third method step, in each case, a deviation volume of the flow volume in one of the flow intervals from a reference flow volume is determined and the deviation volume is compared to a threshold deviation volume. In a fourth method step, if the deviation volume in one of the flow intervals is less than the threshold deviation volume, a zero flow through the measuring tube is determined and compensated using the measured flow in the zero flow interval directly preceding the flow interval. The compensation of the zero flow is carried out, for example, by subtracting the zero flow from the measured flow, whereby the constant measurement error caused by the zero flow is at least reduced.
It can be seen from the first and second method steps that the method according to the invention requires a flow profile of the medium through the measuring tube, in which the measured flow of the medium is in flow intervals greater than or equal to the flow threshold and in zero flow intervals less than the flow threshold. In a first example, the flow profile of the medium in the measuring tube is generated by a calibration device. In a second example, the flow profile is given by the process, in which the flowmeter is integrated. The process is, for example, a filling process of a medium into a container. A filling process consists essentially of a first and a second filling step that is continuously repeated. In the first filling step, a container is filled with the medium in that the medium is conveyed, whereby it also flows through the measuring tube. In the second filling step, the filled container is replaced by a further container, wherein the medium is not conveyed and, thus, does not flow through the measuring tube. Consequently, the flow threshold is chosen so that the first method step of the method according to the invention is carried out during the first filling step of the filling process and the second method step is carried out during the second filling step. Therefore, the method according to the invention is particularly suitable for filling processes.
The fourth method step is based on the insight according to the invention, that the deviation volume of the flow volume in one of the flow intervals from the reference flow volume corresponds to a flow volume in the zero flow interval directly preceding the flow interval. Since a flow volume in a zero flow interval influences the determination of the zero flow, the zero flow is only determined using a flow measured in a zero flow interval when the deviation volume in the flow interval directly following the zero flow interval is less than the threshold deviation volume. Accordingly, the threshold deviation volume corresponds to the deviation of the zero flow from zero, which is why the threshold deviation volume is determined by the tolerable, constant measurement error caused in a process by the zero flow.
In the method according to the invention, the condition for determining the zero flow is that the deviation volume is less than the threshold deviation volume, which is why the method does not require a reference flow volume of a certain amount. Thus, it is provided in a first implementation of the method according to the invention that the reference flow volume is determined from at least one of the flow volumes. The implementation is, in particular, advantageous for filling processes since the filling steps and, thus, also the flow intervals and zero flow intervals are continuously repeated and, hence, a plurality of flow volumes is determined.
In a further development of the previous implementation, it is provided that the reference flow volume is determined in that one of the flow volumes is assigned to the reference flow volume. The assignment of one of the flow volumes to a reference flow volume represents the simplest form of determining the reference flow volume.
Every measurement of a physical quantity, as is carried out for measuring the flow of a medium, is affected by errors. The errors include, in any case, statistically distributed errors such as noise and can also include sporadic errors. The errors are also contained in the flow volumes determined from the flow, which is why they are contained in the reference flow volume in the assignment of one of the flow volumes to the reference flow volumes. Thus, in order to reduce errors in the reference flow volume, it is provided in an alternative further development of the previous implementation that the reference flow volume is determined in that the average value of at least two of the flow volumes is determined and assigned to the reference flow volume.
Each flow interval begins when the measured flow exceeds the flow threshold and ends when the measured flow falls below the flow threshold. Accordingly, each zero flow interval begins when the measured flow falls below the flow threshold and ends when the measured flow exceeds the flow threshold. So that the flow volume determined from the measured flow corresponds to the actual flow volume, the flow threshold is to be assigned to a flow of zero. However, since the measured flow is affected by errors, a flow greater than the errors is to be assigned to the flow threshold, wherein the flow assigned to the flow threshold is usually close to zero.
The flow through the measuring tube normally has a large gradient both when exceeding as well as when falling below the flow threshold, which results in a transient response of the flow. Thus, in order to increase the accuracy and/or constancy of the determination of the flow volume, it is provided in a further implementation of the method that the flow volume, in each case, is determined in a sub-interval of a flow interval. The duration of the sub-interval in one of the flow intervals is thereby measured so that the transient responses of the flow within the flow interval have already subsided. The smaller duration of a sub-interval compared to a flow interval has the effect that a certain flow is smaller than the actual flow, which, however, has no effect on the method according to the invention.
In order to the increase of the accuracy and/or constancy of the determination of the zero flow, respective considerations have led to a further implementation, in which it is provided that, in each case, the measured flow is used in a sub-interval of a zero flow interval. In this implementation, the duration of the sub-interval is also dimensioned so that transient responses of the flow within the sub-interval have already subsided.
The effort of the method according to the invention is reduced in a further implementation in that, in each case, a continuous dwell time of the measured flow less than the flow threshold is assigned to a zero flow interval, if the deviation volume in a flow interval is less than the threshold deviation volume, wherein the zero flow interval directly precedes the flow interval. Accordingly, not every continuous dwell time of the measured flow less than the flow threshold is assigned to a zero flow interval, rather a continuous dwell time of the measured flow less than the flow threshold is assigned to a zero flow interval only when the deviation volume in the following flow interval is less than the threshold deviation volume.
It is provided in a further implementation that the zero flow is determined using the measured flow in one, single zero flow interval. The accuracy of determination of the zero flow, however, is increased when the determination is carried out successively. Thus, it is provided in an implementation alternative to the previous implementation that the zero flow is determined using the measured flow from at least two zero flow intervals in that a moving average is formed from the measured flow in the at least two zero flow intervals or in that a median filter is used on the measured flow in the at least two zero flow intervals.
According to a second teaching, the invention relates to a flowmeter, in which the derived and depicted object is achieved. The flowmeter according to the invention is initially and essentially characterized in that, during operation, the controller stores a flow threshold, a reference flow volume, and a threshold deviation volume. Furthermore, during operation, the controller assigns, in each case, a continuous dwell time of the measured flow greater or equal to the flow threshold to a flow interval and determines a flow volume from the measured flow in the flow interval. It further assigns, in each case, a continuous dwell time of the measured flow less than the flow threshold to a zero flow interval. Furthermore, during operation, the controller determines, in each case, a deviation volume of the flow volume in one of the flow intervals from the reference flow volume and compares the deviation volume to the threshold deviation volume. If the deviation volume in one of the flow intervals is less than the threshold deviation volume, the controller determines and compensates the zero flow through the measuring tube using the measured flow in the zero flow interval directly preceding the flow interval.
The explanations in respect to the method according to the method also hold true for the flowmeter according to the invention.
A design of the flowmeter according to the invention provides that the controller carries out a previously described method according to the invention.
It is provided in a further design that the flowmeter is a magnetic-inductive flowmeter or a nuclear-magnetic flowmeter.
In detail, there is a plurality of possibilities for designing and further developing the method according to the invention and the flowmeter according to the invention.
In one aspect, the present invention provides a method for operating a flowmeter (1) having a measuring tube (2), wherein the flow (d) of a medium (4) through the measuring tube (2) is measured, characterized in that, in each case, a continuous dwell time of the measured flow (d) greater than or equal to a flow threshold (ds) is assigned to a flow interval (ΔtD,1, ΔtD,2) and a flow volume (V1, V2) is determined from the measured flow (d) in the flow interval (ΔtD,1, ΔtD,2), that, in each case, a continuous dwell time of the measured flow (d) less than the flow threshold (ds) is assigned to a zero flow interval (ΔtN,1), that, in each case, a deviation volume of the flow volume (V1, V2) in one of the flow intervals (ΔtD,1, ΔtD,2) from a reference flow volume is determined and the deviation volume is compared to a threshold deviation volume, and that, if the deviation volume in one of the flow intervals (ΔtD,1, ΔtD,2) is less than the threshold deviation volume, a zero flow through the measuring tube (2) is determined and compensated using the measured flow (d) in the zero flow interval (ΔtN,1) directly preceding the flow interval (ΔtD,1, ΔtD,2).
In one aspect, the reference flow volume is determined from at least one of the flow volumes (V1, V2).
In one aspect, the reference flow volume is determined in that one of the flow volumes (V1, V2) is assigned to the reference flow volume.
In one aspect, the reference flow volume is determined in that an average value of at least two of the flow volumes (V1, V2) is determined and assigned to the reference flow volume.
In one aspect, the flow volume (V1, V2), in each case, is determined in a sub-interval of a flow interval (ΔtD,1, ΔtD,2).
In one aspect, the measured flow (d), in each case, is used in a sub-interval (Δt′N,1) of a zero flow interval (ΔtN,1).
In one aspect, in each case, if the deviation volume in one of the flow intervals (ΔtD,1, ΔtD,2) is less than the threshold deviation volume, a continuous dwell time of the measured volume (d) less than the flow threshold (ds) is assigned to a zero flow interval (ΔtN,1), wherein the zero flow interval (ΔtN,1) directly precedes the flow interval (ΔtD,1, ΔtD,2).
In one aspect, the zero flow is determined using the measured flow (d) of at least two zero flow intervals (ΔtN,1), in that a moving average is formed from the measured flow (d) in the at least two zero flow intervals (ΔtN,1) or in that a median filter is used on the measured flow (d) in the at least two zero flow intervals (ΔtN,1).
In one aspect, the present invention provides a flowmeter (1) having a measuring tube (2) and a controller (3), wherein the controller (3) measures the flow (d) of a medium (4) through the measuring tube (2) during operation, characterized in that, during operation, the controller (3) stores a flow threshold (ds), a reference flow volume and a threshold deviation volume, assigns, in each case, a continuous dwell time of the measured flow (d) greater or equal to the flow threshold (ds) to a flow interval (ΔtD,1, ΔtD,2) and determines a flow volume (V1, V2) from the measured flow (d) in the flow interval (ΔtD,1, ΔtD,2), assigns, in each case, a continuous dwell time of the measured flow (d) less than the flow threshold (ds) to a zero flow interval (ΔtN,1), determines, in each case, a deviation volume of the flow volume (V1, V2) in one of the flow intervals (ΔtD,1, ΔtD,2) from the reference flow volume and compares the deviation volume to the threshold deviation volume, and, if the deviation volume in one of the flow intervals (ΔtD,1, ΔtD,2) is less than the threshold deviation volume, determines and compensates the zero flow through the measuring tube (2) using the measured flow (d) in the zero flow interval (ΔtN,1) directly preceding the flow interval (ΔtD,1, ΔtD,2).